Incidence and prognostic implications of heart block complicating inferior myocardial infarction treated with thrombolytic therapy: results from TIMI II.

OBJECTIVES The aim of this study was to determine the incidence and significance of second- or third-degree heart block among patients with inferior myocardial infarction treated with thrombolytic therapy. BACKGROUND Data from the prethrombolytic era suggest that heart block occurs in approximately 20% of patients with acute inferior myocardial infarction and is associated with a marked increase in mortality. Little is known about the incidence and prognostic implications of heart block among patients receiving thrombolytic therapy. METHODS We studied 1,786 patients with acute inferior myocardial infarction enrolled in the Thrombolysis in Myocardial Infarction (TIMI) II Trial who received recombinant tissue-type plasminogen activator (rt-PA) within 4 h of the onset of symptoms. RESULTS Heart block occurred in 214 patients (12%); 113 (6.3%) had heart block on presentation and 101 (5.7%) developed heart block in the 24 h after treatment with rt-PA. Patients with heart block at entry were slightly older and a greater proportion had cardiogenic shock. The 21-day mortality rate among patients with heart block at entry was 7.1% (8 of 113), compared with 2.7% (45 of 1,673) among patients without heart block at study entry (relative risk 2.6, p = 0.007). However, heart block was not independently associated with 21-day mortality after adjustment for other variables, including shock. Mortality and other adverse cardiac events in the following year were similar among patients with and without heart block. Among patients without heart block at study entry, coronary angiography among patients randomly assigned to coronary catheterization 18 to 48 h after admission revealed that the infarct-related artery was occluded in 28.2% (11 of 39) of patients who developed heart block versus 15.5% (112 of 723) of patients without heart block (p = 0.04). The 21-day mortality rate was increased among patients in whom heart block developed after thrombolytic therapy (9.9% [10 of 101] versus 2.2% [35 of 1,572] of patients without heart block, relative risk 4.5, p less than 0.001). Analysis of the increased mortality among patients who developed heart block suggests that mortality was due to severe cardiac dysfunction; no patient was considered to have died as a result of the heart block or its treatment. CONCLUSIONS Heart block is common among patients with inferior infarction given thrombolytic therapy and is associated with increased mortality. These clinical and anatomic data provide insight into the mechanism of heart block and increased mortality among such patients.